Former CIA chief David Petraeus has apologised for the "mistake" that triggered his resignation last year, in his first public speech since quitting due to an extramarital affair.

Addressing a military audience in Los Angeles, the four-star general voiced regret for the "pain" caused by his relationship with his biographer Paula Broadwell, pledging to try to "make amends to those I have hurt and let down".

"I join you keenly aware that I am regarded in a different light now than I was a year ago," General Petraeus told over 600 veterans and military students hosted by the University of Southern California (USC).

"I am also keenly aware that the reason for my recent journey was my own doing.

"So please allow me to begin my remarks this evening by reiterating how deeply I regret - and apologise for - the circumstances that led me to my resignation from the CIA and caused such pain for my family, friends and supporters."

General Petraeus, America's most celebrated military leader in a generation who spearheaded the surge in Iraq, stepped down on November 9 as head of the CIA after admitting to an affair with Ms Broadwell, a counter-terrorism expert and lieutenant-colonel.

The FBI stumbled upon the affair when Jill Kelley, a Florida socialite and friend of the Petraeus family, asked investigators to look into threatening emails that turned out to be from an apparently jealous Ms Broadwell.

The probe that revealed General Petraeus's affair also uncovered potentially "inappropriate" emails between Ms Kelley and the top commander in Afghanistan, General John Allen, although he was later cleared of any wrongdoing.

In the wake of the scandal, General Petraeus has kept a low profile over the past five months.

He has received offers from the financial community and to give paid speeches, been asked to serve as a consultant to major companies and is exploring positions in academia, according to The New York Times.

In his speech, the ex-CIA chief - who was given a standing ovation at the start and end of his remarks - called for greater efforts to help returning veterans transition to civilian life.

Free trade is the oldest argument in federal politics and the issue that literally defined the federation era but opposition exists to the TPP, courtesy of the Investor-State Dispute Resolutions clause.